feat(learn): excerpts and the example store (decision-engine 6.1)

learn/excerpt.py: the labelled function at its pin as numbered lines, bounded
(80 lines / 4,000 chars for candidates, 40 / 2,000 for memory examples),
centred on focus lines; advisory ids anywhere and comments with security
wording (labels.security_reason, multilingual) become <redacted>; owner,
owner/name, path and commit ids are replaced; a delta unit appends the
base->head diff (<= 40 lines). C/C++ and other brace languages without a
repo-facts declaration pattern use a brace matcher (346 c_cpp pair rows
had no excerpt without it).

learn/examples.py + `ousast learn memory build`: label + feature record +
excerpt -> `example` rows (no rationale), excerpts as content-addressed
blobs; refuses origin: user and sources outside sources.toml (exit 2);
conditional labels skipped; exit 2 when >10% of a source's recorded
candidates have no excerpt. A fixed side that was read but no longer
declares the labelled function is counted apart (absent_fixed_side): a
label defect, not an unread clone.

plane/memory.py: `example` in KINDS; put_blob/get_blob/blob_names on the
MemoryStore base, so FileStore and MinioStore share them (tested on both,
MinIO through the fake object client).

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

.kiro/specs/learned-decision-engine/tasks.md

@@ -38,7 +38,7 @@ a model or embedding call.
   - _Requirements: 1.1_
 
 - [ ] 6. Program, local memory and compilation (design sections 4-5)
-  - [ ] 6.1 Excerpts and the example store (no model)
+  - [x] 6.1 Excerpts and the example store (no model)
     - `learn/excerpt.py` (function span at the label's pin, bounds 80/4,000 for candidates and 40/2,000 for
       examples, numbered lines, no path/repository/commit, advisory ids and security wording in comments
       redacted, delta diff); `learn/examples.py` and `ousast learn memory build` (label + feature record +